docs: def delta_to_str(rd):
      """ Convert a relativedelta to a human-readable string """
      parts = []
      if rd.days > 0:
          parts.append("%d day%s" % (rd.days, plural(rd.days)))
      clock_parts = []
      if rd.hours > 0:
          clock_parts.append("%02d" % rd.hours)
      if rd.minutes > 0 or rd.hours > 0:
          clock_parts.append("%02d" % rd.minutes)
      if rd.seconds > 0 or rd.minutes > 0 or rd.hours > 0:
          clock_parts.append("%02d" % rd.seconds)
      if clock_parts:
          parts.append(":".join(clock_parts))
      return " ".join(parts)